Re: [PATCH v3 4/9] x86/kvm/mmu: introduce guest_mmu

From: Sean Christopherson
Date: Fri Oct 05 2018 - 15:23:11 EST

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On Mon, Oct 01, 2018 at 04:20:05PM +0200, Vitaly Kuznetsov wrote:
> When EPT is used for nested guest we need to re-init MMU as shadow
> EPT MMU (nested_ept_init_mmu_context() does that). When we return back
> from L2 to L1 kvm_mmu_reset_context() in nested_vmx_load_cr3() resets
> MMU back to normal TDP mode. Add a special 'guest_mmu' so we can use
> separate root caches; the improved hit rate is not very important for
> single vCPU performance, but it avoids contention on the mmu_lock for
> many vCPUs.
>
> On the nested CPUID benchmark, with 16 vCPUs, an L2->L1->L2 vmexit
> goes from 42k to 26k cycles.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>

One nit below, otherwise:

Reviewed-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

> ---
> Changes since v2:
> - move kvm_mmu_free_roots() call to nested_release_vmcs12().
> [Sean Christopherson]
> - in kvm_calc_shadow_ept_root_page_role() we need to inherit role
> from root_mmu so fields like .smap_andnot_wp, .smep_andnot_wp, ...
> remain correctly initialized [pointed out by Sean Christopherson]
> ---
> arch/x86/include/asm/kvm_host.h | 3 +++
> arch/x86/kvm/mmu.c | 18 +++++++++++++----
> arch/x86/kvm/vmx.c | 35 +++++++++++++++++++++------------
> 3 files changed, 39 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 404c3438827b..a3829869353b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -539,6 +539,9 @@ struct kvm_vcpu_arch {
> /* Non-nested MMU for L1 */
> struct kvm_mmu root_mmu;
>
> + /* L1 MMU when running nested */
> + struct kvm_mmu guest_mmu;
> +
> /*
> * Paging state of an L2 guest (used for nested npt)
> *
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 9cb2f9307e98..bb6584222848 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -4818,6 +4818,9 @@ kvm_calc_shadow_ept_root_page_role(struct kvm_vcpu *vcpu, bool accessed_dirty)
> {
> union kvm_mmu_page_role role = vcpu->arch.mmu->base_role;

@role is initialized by the new code below, this can be removed,
e.g. it's eventually removed by patch 7/9 when the two pieces of
the combined role are initialized independently.

> + /* Role is inherited from root_mmu */
> + role.word = vcpu->arch.root_mmu.base_role.word;
> +
> role.level = PT64_ROOT_4LEVEL;
> role.direct = false;
> role.ad_disabled = !accessed_dirty;
> @@ -4966,8 +4969,10 @@ EXPORT_SYMBOL_GPL(kvm_mmu_load);
>
> void kvm_mmu_unload(struct kvm_vcpu *vcpu)
> {
> - kvm_mmu_free_roots(vcpu, vcpu->arch.mmu, KVM_MMU_ROOTS_ALL);
> - WARN_ON(VALID_PAGE(vcpu->arch.mmu->root_hpa));
> + kvm_mmu_free_roots(vcpu, &vcpu->arch.root_mmu, KVM_MMU_ROOTS_ALL);
> + WARN_ON(VALID_PAGE(vcpu->arch.root_mmu.root_hpa));
> + kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu, KVM_MMU_ROOTS_ALL);
> + WARN_ON(VALID_PAGE(vcpu->arch.guest_mmu.root_hpa));
> }
> EXPORT_SYMBOL_GPL(kvm_mmu_unload);
>
> @@ -5406,13 +5411,18 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu)
>
> vcpu->arch.mmu = &vcpu->arch.root_mmu;
> vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
> +
> vcpu->arch.root_mmu.root_hpa = INVALID_PAGE;
> vcpu->arch.root_mmu.translate_gpa = translate_gpa;
> - vcpu->arch.nested_mmu.translate_gpa = translate_nested_gpa;
> -
> for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++)
> vcpu->arch.root_mmu.prev_roots[i] = KVM_MMU_ROOT_INFO_INVALID;
>
> + vcpu->arch.guest_mmu.root_hpa = INVALID_PAGE;
> + vcpu->arch.guest_mmu.translate_gpa = translate_gpa;
> + for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++)
> + vcpu->arch.guest_mmu.prev_roots[i] = KVM_MMU_ROOT_INFO_INVALID;
> +
> + vcpu->arch.nested_mmu.translate_gpa = translate_nested_gpa;
> return alloc_mmu_pages(vcpu);
> }
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 9a3aece131fb..73f04a8638d3 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8442,8 +8442,10 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx)
> vmcs_write64(VMCS_LINK_POINTER, -1ull);
> }
>
> -static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
> +static inline void nested_release_vmcs12(struct kvm_vcpu *vcpu)
> {
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> +
> if (vmx->nested.current_vmptr == -1ull)
> return;
>
> @@ -8457,10 +8459,12 @@ static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
> vmx->nested.posted_intr_nv = -1;
>
> /* Flush VMCS12 to guest memory */
> - kvm_vcpu_write_guest_page(&vmx->vcpu,
> + kvm_vcpu_write_guest_page(vcpu,
> vmx->nested.current_vmptr >> PAGE_SHIFT,
> vmx->nested.cached_vmcs12, 0, VMCS12_SIZE);
>
> + kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu, KVM_MMU_ROOTS_ALL);
> +
> vmx->nested.current_vmptr = -1ull;
> }
>
> @@ -8468,8 +8472,10 @@ static inline void nested_release_vmcs12(struct vcpu_vmx *vmx)
> * Free whatever needs to be freed from vmx->nested when L1 goes down, or
> * just stops using VMX.
> */
> -static void free_nested(struct vcpu_vmx *vmx)
> +static void free_nested(struct kvm_vcpu *vcpu)
> {
> + struct vcpu_vmx *vmx = to_vmx(vcpu);
> +
> if (!vmx->nested.vmxon && !vmx->nested.smm.vmxon)
> return;
>
> @@ -8502,6 +8508,8 @@ static void free_nested(struct vcpu_vmx *vmx)
> vmx->nested.pi_desc = NULL;
> }
>
> + kvm_mmu_free_roots(vcpu, &vcpu->arch.guest_mmu, KVM_MMU_ROOTS_ALL);
> +
> free_loaded_vmcs(&vmx->nested.vmcs02);
> }
>
> @@ -8510,7 +8518,7 @@ static int handle_vmoff(struct kvm_vcpu *vcpu)
> {
> if (!nested_vmx_check_permission(vcpu))
> return 1;
> - free_nested(to_vmx(vcpu));
> + free_nested(vcpu);
> nested_vmx_succeed(vcpu);
> return kvm_skip_emulated_instruction(vcpu);
> }
> @@ -8539,7 +8547,7 @@ static int handle_vmclear(struct kvm_vcpu *vcpu)
> }
>
> if (vmptr == vmx->nested.current_vmptr)
> - nested_release_vmcs12(vmx);
> + nested_release_vmcs12(vcpu);
>
> kvm_vcpu_write_guest(vcpu,
> vmptr + offsetof(struct vmcs12, launch_state),
> @@ -8923,7 +8931,8 @@ static int handle_vmptrld(struct kvm_vcpu *vcpu)
> return kvm_skip_emulated_instruction(vcpu);
> }
>
> - nested_release_vmcs12(vmx);
> + nested_release_vmcs12(vcpu);
> +
> /*
> * Load VMCS12 from guest memory since it is not already
> * cached.
> @@ -10976,12 +10985,10 @@ static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)
> */
> static void vmx_free_vcpu_nested(struct kvm_vcpu *vcpu)
> {
> - struct vcpu_vmx *vmx = to_vmx(vcpu);
> -
> - vcpu_load(vcpu);
> - vmx_switch_vmcs(vcpu, &vmx->vmcs01);
> - free_nested(vmx);
> - vcpu_put(vcpu);
> + vcpu_load(vcpu);
> + vmx_switch_vmcs(vcpu, &to_vmx(vcpu)->vmcs01);
> + free_nested(vcpu);
> + vcpu_put(vcpu);
> }
>
> static void vmx_free_vcpu(struct kvm_vcpu *vcpu)
> @@ -11331,6 +11338,7 @@ static int nested_ept_init_mmu_context(struct kvm_vcpu *vcpu)
> if (!valid_ept_address(vcpu, nested_ept_get_cr3(vcpu)))
> return 1;
>
> + vcpu->arch.mmu = &vcpu->arch.guest_mmu;
> kvm_init_shadow_ept_mmu(vcpu,
> to_vmx(vcpu)->nested.msrs.ept_caps &
> VMX_EPT_EXECUTE_ONLY_BIT,
> @@ -11347,6 +11355,7 @@ static int nested_ept_init_mmu_context(struct kvm_vcpu *vcpu)
>
> static void nested_ept_uninit_mmu_context(struct kvm_vcpu *vcpu)
> {
> + vcpu->arch.mmu = &vcpu->arch.root_mmu;
> vcpu->arch.walk_mmu = &vcpu->arch.root_mmu;
> }
>
> @@ -13422,7 +13431,7 @@ static void vmx_leave_nested(struct kvm_vcpu *vcpu)
> to_vmx(vcpu)->nested.nested_run_pending = 0;
> nested_vmx_vmexit(vcpu, -1, 0, 0);
> }
> - free_nested(to_vmx(vcpu));
> + free_nested(vcpu);
> }
>
> /*
> --
> 2.17.1
>

Next message: Joel Fernandes (Google): "[PATCH RFC] mm: Add an fs-write seal to memfd"
Previous message: Bjorn Andersson: "Re: [PATCH V3 1/4] rpmsg: core: Add signal API support"
In reply to: Vitaly Kuznetsov: "[PATCH v3 4/9] x86/kvm/mmu: introduce guest_mmu"
Next in thread: Vitaly Kuznetsov: "[PATCH v3 5/9] x86/kvm/mmu: get rid of redundant kvm_mmu_setup()"
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